Up to the present time, fermentations requiring a high rate of oxygen input, such as high cell density fermentation processes disclosed in U.S. Pat. No. 4,414,329 by Wegner (assigned to Phillips Petroleum Co.), have been generally conducted in fermentation vessels equipped with agitation means and mechanical defoamer means. The patent literature disclosing such fermentors includes: U.S. Pat. Nos. 4,670,397, 4,752,564, 4,883,759, 4,373,024. Agitated fermentors are difficult to adapt to supply the very high rate of oxygen input, necessary to conduct high cell density fermentation processes for large scale plants, and for various physical and biological reasons, it is not commercially feasible to increase the size of those vessels beyond certain limits. Stirrers and mechanical foam breakers employed in high cell density fermentations require very high energy input, which is both, costly and a major problem in large fermentors. Problems of drive shaft and bearing design for transmitting the enormous torque arise. In addition, seals associated with the stirrer and the foam breaker are often difficult to clean and sterilize and in many instances create cleaning and asepsis problems. Consequently, there is a continuing need for improved fermentors of even larger capacity than those built to date, and capable of conducting aerobic fermentation processes at high cell densities and high productivities. At the same time, a fermentor which does not require moving parts for effective foam control, which is simple in construction, economical to manufacture and to maintain, and which gives good results in terms of achievable oxygen transfer rate and power consumption would provide obvious advantages.
Fermenters having non mechanical agitation and/or non mechanical foam control means are a desirable alternative to mechanically agitated systems. Potential advantages are as follows: Improved maintenance of sterility because no top and bottom entering shafts, construction of larger fermentors is possible because the design is not limited by motor size and shaft length and weight, the fermentors are cheaper to fabricate since no agitator, gear box or crane rail is needed, less structural steel is used, better energy efficiency and reduced maintenance. Our invention thus is intended to provide a fermentor and a fermentation method which overcome several shortcomings of fermentors and fermentation methods of the present technology.